1. Field of Invention
This invention is related generally to devices for pumping liquids, and more particularly, to external gear pumps used to pump liquids.
2. Description of Related Art
Typically, external gear pumps have two or more gears that may or may not have the same number of teeth. Most commonly the gears have the same number of teeth, although the gears are not limited thereto. Whether or not the gears have the same number of teeth, it is the speed of the drive gear that determines the liquid flow rate or volumetric capacity from a given pump. Therefore, the traditional method used to change the flow produced from a given pump was to change the drive gear speed.
European Publication EP/685650 A1 discloses a gear pump which fits into a cavity at a plurality of selected positions for defining distinct chambers with different axial extensions adapted to accommodate pairs of gearwheels with different axial dimensions. This provides the apparatus with a plurality of pump or motor configurations suitable for achieving a selected one of a plurality of different displacements and fluid inlet and outlet configurations. European Publication EP/445584 A1, and its corresponding U.S. Pat. No. 5,161,961 to Zheng, describes multiple equivalent pumps or motors can be made by using multiple external gears and internal gears, which are engaged with each other, along with multiple radial sealing elements, and axial sealing elements.
Many companies, including Roper Pump Company, have made pumps with two different size gears for years. However, it would be a benefit to be able to build two different pumps with different volumetric displacements from one set of parts. It would be another benefit to be able to change the flow rate or volumetric capacity of a pump without changing either the speed or the parts in the pump. All references cited herein are incorporated herein by reference in their entireties.